1. 2 Dr.Wahid Helmy pediatric consultant. Basics of Mechanical Ventilation in Neonates.

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Dr.Wahid Helmypediatric consultant.

Basics of Mechanical Ventilation in Neonates

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Prevention of alveolar collapse ◘Functional residual capacty (FRC).

◘Surfactant.

◘ Elatic-recoil ( compliance).

◘Intrapleural pressure(-4mmHg) during inspiration and (+4mmHg) during inspiration.

◘If surfactant is absent , Intrapleural pressure negativity may be increased up to (-20mmHg) .

What is it?

Pulmonary MechanicsPulmonary Mechanics

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1)Tidal Volume )Vt)

◘Air inspired or expired in one breath.

◘ (Vt) = 6-10 mL/kg/Breath.

◘ RR is usually 30-60 BPM.

◘ minute volume = (Vt- Dead space)x RR.

◘ Tidal Volume is proportional to (PIP) and

to Dynamic Lung Compliance.

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2)Compliance = 0.004 L/cmH2O.

◘Elastic - recoil properties of the lung and chest wall.

◘ Estimated from simultaneous changes in volume and pressure.

◘ Compliance )mL/cmH2O)-:

= Change in volume (mL) = 0.004 L/cmH2O.

Change in pressure(cmH2O)

3)Resistance = 30cm H2O/L/sec

◘Describes property of the lungs that resists airflow

–Airway resistance.

–Tissue resistance.

◘ Resistance = Change in pressure (cmH2O)

Change in flow (L/sec)

◘Resistance during inspiration < during expiration.

4)one Time constant = Resistance X Compliance4)one Time constant = Resistance X Compliance

◘ one time constant → 63% equilibration of pressure inside & outside the alveoli.

◘ we need 3 time constant →97% equilibration of pressure inside & outside the alveoli.

◘ Time constant = Time constant = Resistance X ComplianceResistance X Compliance

4) Time constant ,cont.,4) Time constant ,cont.,

◘ Time constant = Resistance X ComplianceTime constant = Resistance X Compliance◘ ExampleExample• If resistance =30cm H2O/L/sec • compliance = 0.004 L/cmH2O.• One time constant =30 X 0.004 = 0.12 seconds.• We need 3time constant to inflate and deflate the lung

(3 X 0.12 seconds = 0.36 seconds=Ti ).• as aresult Te= 2 or 3 X 0.36seconds.• So I/E ratio = 1:2 or 1:3 .

Types of Mechanical Types of Mechanical VentilatorsVentilators

Types of Mechanical Ventilators

• Volume-cycled ventilators.

• Pressure ventilators .

• Pressure-limited, time-cycled, continuous-flow ventilators

• Patient–triggered ventilators (PTV).

Pressure-Limited, Time-Cycled, Continuous-Flow VentilatorsPressure-Limited, Time-Cycled, Continuous-Flow Ventilators

• You select (PIP)→ (pressure-limited).

• You select inspiratory time → (time-cycled).

• )Continuous flow) →Fresh heated humidified gas is delivered to the patient throughout the respiratory cycle.

What is it?

Parameters of mechanical Parameters of mechanical ventilationventilation

Peak Inspiratory Pressure )PIP)

• The maximum pressure reached during inspiration.

• If PIP is too low → low VT.• If PIP too high → high VT →

–Barotraumas and BPD–Hyperinflation and air leak–Impedance of venous return

•↑↑↑ tidal volume, is more injurious to the lung than ↑↑↑ (PIP).

PEEP

• (Optimum (PEEP) is 4-6 cmH2O).• Optimum (PEEP) →prevent lung collapse and maintain

stability of the alveoli.• below Optimum (PEEP) lung volume is not maintained.

• High PEEP >8 cmH2O

–Reduces gradient between PIP & PEEP→ (↓ VT) .

–Decreases venous return .

–Increases pulmonary air leaks .

–Produces CO2 retention .

)FiO2( • Increase in FiO2 alters alveolar oxygen tension,

provides a larger diffusion gradient, and improves oxygenation.

• Oxygen and Paw should be balanced to minimize lung damage.

• During weaning, Paw should be reduced before a very low FiO2 is reached. If PIP is not decreased until a low FiO2 is reached, a high incidence of air leak is observed.

RR, secrets• ↑ RR → ↑ (CO2 wash).

• RR(60 BPM) allows for PIP reduction in PIP → ↓ incidence of pneumothorax with about 50% .

• Most neonates have short time constants. can tolerate (RR60-70 Bpm) and short (Te) without marked gas trapping .

• Determines minute ventilation(RR×VT), thusCO2 elimination.

Ti and Te

InspiratoryInspiratory Time (Ti)Time (Ti)

Usually adjusted between 0.35-0.6 second

Depends on the pulmonary mechanics:

–Compliance . –Resistance . –Time constant.

I:E ratio

• I:E ratio should NOT be less than 1:1.2

• It should NOT be reversed

• Ti of 1.0 second or longer → active expiration, fighting the ventilator, slower weaning, and a high incidence of pneumothorax.

Flow

• Volume of gas passed / time unit (liter/minute).

• Flow rates of 6-10 liter/min are usually sufficient.

• High flows can lead to turbulence, an increase in resistance, and gas trapping .

mean airway pressure• It is ameasure of the average pressureto

which lungs are exposed during the respiratory cycle.

• It is the factor (other than FiO2) that determines oxygenation.

• An ↑ in PIP and PEEP→ ↑ oxygenation more than ↑ in the I:E ratio.

• NB., ↑ ↑ ↑ Paw →alveolar over distension with right to left shunt.

Pressure gradient

Peak inspiratory pressure )PIP):Peak inspiratory pressure )PIP):• pressure gradient berween (PIP) & (PEEP)

affects alveolar ventilation.• Increase in PIP will:

– ↑ tidal volume.– ↑ CO2 wash.– ↑ Paw which improve oxygenation.

Minute alveolar ventilationMinute alveolar ventilation

Minute alveolar ventilationMinute alveolar ventilation

= )Tidal volume – = )Tidal volume – Dead space) X Frequency.Dead space) X Frequency.

• Tidal volume,is determined mainly with Tidal volume,is determined mainly with pressure gradient betweenpressure gradient between inspiration and inspiration and expiration expiration i.e. (PIP) minus (PEEP).

Gas Exchange during Assisted Ventilation

Carbon dioxide )CO2) ExchangeCarbon dioxide )CO2) Exchange• It depends on Alveolar ventilation.

• Diffuses rapidly from the blood into the alveoli. OxygenExchangeOxygenExchange

• Oxygen exchange depends largely on the matching of perfusion with ventilation.

Modes of venilation

Who is the Commande?

A)A) Non-triggeredNon-triggered Modes.Modes.الطفل تنفس لمعدل النظر دون الجهاز بواسطة والضغط التنفس معدل تحديد الطفل يتم تنفس لمعدل النظر دون الجهاز بواسطة والضغط التنفس معدل تحديد يتم

1.Controlled Mandatory Ventilation )CMV) or IPPV: – IPPV (intermittent positive pressure ventilation ).

–Ventilator rate is set > infant's spontaneous.

– RR (usually 50-80 breaths/min).

2.Intermittent Mandatory Ventilation )IMV):– Ventilator rate is set < infant's spontaneous breaths.

– RR (<30 breaths/min).

– spontaneous breaths above the set rate are not assisted.

◙Infant’s respiratory drive and rhythm determine the rate of ventilation.1.Assist/Control )A/C) - Synchronized Intermittent Positive Pressure Ventilation )SIPPV 2.Synchronized Intermittent Mandatory Ventilation )SIMV).

3.Pressure Support Ventilation )PSV)4.Volume Guarantee )VG) ventilation.

◙ VolumeVolume GuaranteeGuarantee )VG))VG) ventilationventilation◙ Pressure-controlled ventilationIt delivers a preset VT, this volume is continuously monitored by the ventilator and the pressure may increase or decrease to guarantee the target VT.Addition of VG to A/C or SIMV results in:–Less risk of volutrauma–Auto-weaning of PIP )may reduce barotraumas

B)B) Patient-triggeredPatient-triggered VentilationVentilation (PTV(PTV))

Patient–Triggered Ventilators )PTV)

• Modification of conventional ventilation .

• the patient is able to initiate ventilator breaths.

• There is a sensor of thoracoabdominal movement, airflow, or airway pressure to indicate the onset of the inspiratory efforts, and so triggering the ventilator setting.

Patient–Triggered Ventilators )PTV) )cont.)

• If the infant does not generate an adequate inspiratory effort during a preset period, the ventilator will deliver a nontriggered breath.

• Result in improved tidal volume and blood gases but may lead to hyperventilation in tachypneic infants.

Patient–Triggered Ventilators )PTV) )cont.)

PTV is used in two modes:PTV is used in two modes:

1. Synchronized Intermittent Mandatory Ventilation (SIMV)– A single triggered breath is given in equal windows

of time, with the other patient breaths occurring during each window not assisted.

– This way the rate can be slowly reduced with all assisted breaths well-synchronized.

Assist / Control mode (sippv) (A/C)

2. Assist / Control mode (A/C)– All breaths are triggered, the patient controls the

ventilator rate, and weaning is accomplished by reducing the PIP.

– Advantage is reduction in cerebral blood flow variability.

– Weaning from ventilator is facilitated in both A/C and SIMV.

– These ventilators reduce the duration of assisted ventilation and facilitate weaning.

Indications of Mechanical Ventilation

Absolute indicationsAbsolute indications

If any of the following is present:If any of the following is present:

1. Severe hypoxemia with PaO2 less than 50 mmHg despite FiO2 of 0.8.

2. Respiratory acidosis with pH of less than 7.20 to 7.25, or PaCO2 above 60 mmHg.

3. Severe prolonged apnea.

Indications of Mechanical Ventilation )cont.)

Relative indicationsRelative indications1. Frequent intermittent apnea unresponsive to

drug therapy.2. Early treatment when use of mechanical

ventilation is anticipated because of deteriorating gas exchange.

3. Relieving work of breathing in an infant with signs of respiratory difficulty.

4. Initiation of exogenous surfactant therapy in infants with RDS.

Blood Gases Changes by Ventilator Setting

EffectEffectVentilator setting Ventilator setting

changeschangesPaCO2PaCO2 PaO2PaO2

Increase PIPIncrease PIP Decrease Increase

Increase PEEPIncrease PEEP Increase Increase

Increase rateIncrease rate Decrease Increase

Increase I:E ratioIncrease I:E ratio ------- Increase

Increase FiO2Increase FiO2 ------- Increase

Increase flowIncrease flow Decrease Increase

ET Size

Infant weight)gm)Infant weight)gm) Endotracheal tube Endotracheal tube internal diameterinternal diameter

< 1,000gm 2.5mm

1,000 - 2,000 3.0mm

2,000 - 3,000 3.5mm

> 3,000 3.5 - 4.00mm

Initial Setting of Mechanical Ventilation

Initial settingsInitial settings

Fio2Fio2 As indicatedAs indicated

Systemic flowSystemic flow 8-10l/min8-10l/min

RateRate 60 breaths / min60 breaths / min

Ti/TeTi/Te 1:2 - 1:31:2 - 1:3

PIPPIP 18 - 22cm H2018 - 22cm H20

Good breath soundsGood breath sounds

PEEPPEEP 3 - 5cm H203 - 5cm H20

Subsequent settingsSubsequent settings PEEPPEEP PIPPIP

Low PaO2 ,Low PaO2 ,

Low PaCo2Low PaCo2Increase

Low PaO2 ,Low PaO2 ,

High PaCo2High PaCo2

Increase

High PaO2 ,High PaO2 ,

High PaCo2High PaCo2

Decrease

High PaO2 ,High PaO2 ,

Low PaCo2Low PaCo2

Decrease

Monitoring The Infant during Mechanical Ventilation

• Obtain an initial blood gas within 15-30 minutes of starting mechanical ventilation.– Obtain a blood gas within 15-30 minutes of any

change in ventilator settings. – Obtain a blood gas every 6 hours unless a sudden

change in the infant's condition occurs.

– Continuous monitoring of the O2 saturation level as

well as the HR and RR is necessary.

Deterioration during Mechanical Ventilation

Sudden clinical deteriorationSudden clinical deterioration• Mechanical or electrical ventilator failure.• Disconnected tube or leaking connection.• Endotracheal tube displacement or

blockage.• Pneumothorax.

Gradual deteriorationGradual deterioration• Inappropriate ventilator setting.• Intraventricular hemorrhage.• Baby fighting against ventilator.• PDA.• Anemia.• Infection.

Paralysis and Sedation The use of neuromuscular blockade is not

routinely indicated.

It has been advocated in infants requiring mechanical ventilation with a high rate or pressure, and who become increasingly agitated when their spontaneous respiration is out of phase with the ventilator, resulting in decreased effectiveness of mechanical support.

Paralysis and Sedation (cont.)

Paralysis may worsen oxygenation in infants with RDS as it may result in decreased dynamic lung compliance, increased airway resistance, and the removal of the infant’s respiratory effort contribution to tidal breathing.

As a result, it is necessary to increase ventilator pressure after initiation of neuromuscular blockade.

Weaning• FiO2 and PIP are weaned first.• Decrease PIP as tolerated and as chest rise

diminishes.• When PIP is around 20, attention is directed to

FiO2 and then to the respiratory rate alternating with each other, in response to assessment of chest excursion, blood gas results, and oxygen saturation.

Weaning (cont.)

• As frequency is decreased, Te should be prolonged.

• weaning to endotracheal CPAP may begin when PIP has been stable between 15-18 cmH2O, and FiO2 is less than 0.4.

• The infant can be weaned to oxygen hood when he/she requires less than 4 cmH2O of end expiratory pressure.

Weaning (cont.)

• Atelectasis after extubation is common in preterm infants recovering from RDS. Use of nasal CPAP may prevent atelectasis.

• Steroids are not routine before extubation, but if there was prolonged intubation or previous failed attempts of extubation, a short course of steroids may facilitate extubation.

• If strider caused by laryngeal edema develops after extubation, racemic epinephrine aerosols and steroids may be helpful.

Ventilator care requires a team effort. Everyone involved has toget along and trust one another!